Tabbing to create new cell in WPF

This seems like it should be simple, but I'm stumped. So I have a data grid on my form. When I click into a cell it creates a new row. Great, that's exactly what I want to happen. When I tab from the last column of the second
to last row, into the next row, it does not create a new row as I'd expect. Not a big deal until I get to the last column of the last row. Pressing tab does nothing. The expected behavior is that it will create a new row and tab into it.
I'm a bit confused on how to implement this. Any tips?